Deep drawing steel



UnitedStates Patent DEEP DRAWING STEEL Eric R. Morgan, Dearborn, and John C. Shyne, Belleville, Mich., assignors to Ford Motor Company, Dearborn, Mich., a corporation of Delaware No Drawing. Application July 24, 1956, Serial No. 599,677

2 Claims. (Cl. 75-123) This invention is directed to deep drawing steels and more especially to rimmed or semi-rimmed steels possessing superior ductility and resistance to aging. This application is a continuation in part of application Serial No. 497,462 filed March 28, 1955.

Steels which are intended for subsequent deep drawing are conventionally produced by a rimming or semirimming process to secure the desired high quality of surface finish usually required of deep drawn products. These rimmed or semi-rimmed steels are subject to undesirable aging phenomena which are manifested by the appearance of a pronounced yield point and the progressive deterioration of ductility. This aging process occurs even at winter temperatures and often results in a particular batch of steel which was acceptable commercially as produced deteriorating before use to a point where deep drawing operations are impossible.

We have discovered that the addition of boron to steel to give a boron content of between 0.003% to 0.02% will yield a product which will not lose its ductility or exhibit a yield point due to storage under usual commercial conditions. The addition of this minute amount of boron does not interfere with the rimming action necessary to get a good surface finish. The boron may be added as elemental boron, boron carbide, calcium-boride or ferroboron.

To more clearly demonstrate the operation of this invention, three heats were prepared with as nearly identical chemistry as possible. The melts were produced from the pure elements under identical melting condition. The first melt was a steel containing 0.08% carbon and 0.005% nitrogen. The second melt was identical except for the addition of 0.04% vanadium. This heat is typical of good commercial practice using the teachings of Epstein contained in United States Letters Patent 2,356,- 450. In the third melt the vanadium was replaced with 0.02% boron. The physical properties of the steels resulting are tabulated below. Note the high ductility and absence of yield point in the boron treated steel.

2,772,154 Patented Nov. {27, 1956 of carbon rod, grams of ferromanganese and suflicient borax to represent an addition of 0.02% boron. When the melt down was complete and the temperaturehad reached 2900 degrees Fahrenheit themetalwas 'poi red into a ladle containing the 'bora'ir addition. This heat was made to check information contained in the following publications which deal with the reduction of borax to boron by steel or iron from supernatant slags.

Twenty-fifth Open Hearth Proceedings, 1942, pages 109 and 110. Published by the A. I. M. E., New York.

Transactions, American Institute of Mining and Metallurgical Engineers, 1946, vol. 167, pages 92 to 107. Published by the Institute, New York.

Iron and Steel Institute, vol. 171 of the 1952 Journal, pages 147 to 153.

University of Illinois Engineering Experimental Station Bulletin 77, March 1917, vol. 7, pages 1-19.

This procedure resulted in a steel having a boron content of 0.0016% which was inadequate to inhibit aging.

A 200 ton commercial open hearth heat was then prepared having the following ladle analysis.

This heat was tapped into a 200 ton ladle and teemed into 13 ton ingot molds. The characteristics of four of these 13 ton ingots is tabluated below:

Increase in Elonga- Yleld Ultimate tion, Percent Ingot Boron Strength Strength Percent Yield,

Content During (p. s. i.) in 2 Slab/Ingot Aging Inches (p. s. 1.)

A Nil 7, 750 51, 400 27. 7 89. 81 B 1 0. 008 550 42, 650 43. 5 88. 63 0.0067 250 43, 750 40. 5 88. 12 0.008 500 43, 850 42. 0 88.38

The physical data tabulated above was obtained from material which was hot rolled down to 0.100 inch strip and then cold rolled to a thickness of 0.040 inch. The cold rolled sheet was annealed at 1320 degrees Fahrenheit using a conventional boxannealing heating schedule. Tension test specimens of the finished sheet steel were prestrained 10% in tension and then aged one hour at degrees centigrade and retested to failure.

Room Temperature Tensile Tests 0.08% O, 0.005% N; 0.08% O, 0.005% Ni, 0.04% V 0.08% C, 0.005% Ni, 0.02% B Condition of Test Sample Percent Yield Elonga- Percent Yield Elonga- Percent Yield Elonga- Elonga- Strength, tion at Elouga- Strength, tion at Elonga- Strength, tion at tion 1,000 Yield tion 1,000 Yield tion 1,000 Yield 1). s. i. Point p. s. 1. Point p. s. i. Point Annealed 47 38 3. 75 56 41.9 6.0 58 33.2 5 0 Prestrained 7.5% and not aged 39. 5 39. 15 0 48. 5 37. 5 0 50. 5 31. 1 0 Prestrained 7.5% and aged for 1 hr.

at 100 C 25. 2 47. 5 2. 0 42. 0 36. 2 0 51 33. 0 0 Prestrained 7.5% and aged for 2 hrs. at 50 C 46.3 1.1 35.9 0 31. 1 0 Prestraiued 7.5% and aged for 100 hrs. at 25 C 30 50. 8 2. 2 40.7 36. 5 0 50 31. 0 0

An attempt was made to obtain the requisite boron by adding borax directly to a steel melt. The melting charge comprised 50 pounds of electrolytic iron, 20 grams We claim as our invention: 1. A rimmed steel which is non-aging under usual conbetween 0.003 percent and 0.02 percent carbon.

2. A rimmed steel which is non-aging under usual conditions of commercial storage, said steel containing approximately 0.008 percent boron.

References Cited in the file of this patent Twenty-fifth Open Hearth Proceedings, 1942, pages 109 and 110. Published by the A. T. M. 13., New York.

o 4 r a Transactions, American Institute of Miningand- Metallurgical Engineers, 1946, volume 167, pages 92 to 107. Published by the Institute, New York;

Effect of Boron on the Hardenability of I-Iigh Purity Alloys and Commercial Steel. Bureau of Standards Research paper R. P. 1938, vol. 41, 'Dec. 1948, pages 546 and 547. L 

1. A RIMMED STEEL WHICH IS NON-AGING UNDER USUAL CONDITIONS OF COMMERCIAL STORAGE, SAID STEEL CONTAINING FROM BETWEEN 0.003 PERCENT AND 0.02 PERCENT CARBON. 